Experimental Study On The Laser Welding Of Magnesium And Aluminum Dissimilar Metal

Magnesium alloy and aluminum alloy are widely used in the fields of aerospace,automobile,3C products and modern weapons industry for their advantages,such as low density,high specific strength,easy recovery.Because of the great differences in both their physical and chemical properties,the welding of Mg and Al alloy is full of challenge.In this paper,the laser welding was applied to joining AZ31 B magnesium alloy to 5083 aluminum alloy with or without adding of Zinc interlayer.The characteristics of laser welding of Mg/Al dissimilar metals were analyzed.Meanwhile,the effects of Zinc interlayer on the microstructure and the mechanical properties of the joint were investigated.On the basis of experiment,the differences of properties about the ductility and the thermodynamic of the main compounds in the weld were analyzed.And the mechanism of the influence of the Zinc interlayer on the welding of Mg/Al was elaborated.The main results are as follows:?1?When the laser is directly used for the Mg/Al lap joint,the joint of the surface forming quality and the mechanical property is obtained in the processing parameters: P=1.8kW,V=5.5m/min,?f=2mm,by optimizing the orthogonal experiment.There are three kinds of welding modes in the process of laser welding,including deep melt,metastable state and heat conduction,which correspond to different shape of molten pool.For the joints produced by the mode of deep melt,the microstructure on Mg side consisted of ?-Mg,arborization Al₁₂Mg₁₇,while on Al side the microstructure consisted of ?-Al and Al₃Mg₂.The fracture occurred in the transition zone of continuous Mg-Al IMCs layers with an average tensile-shear strength about 591.4N;For the metastable-welding joints,the microstructure of the joints indicated a high degree of mixing with multiple interfaces of Mg to Al formed in the weld.The fracture occurred in the Al₁₂Mg₁₇ layers near the fusion zone on Mg side and the average tensile-shear strength reached 772.2N;For the joints produced by the mode of heat conduction,the microstructure on Mg side was homogeneous and the continuous Al₁₂Mg₁₇ and Al₃Mg₂ IMCs layer was formed in 475.1N.?2?With the increase of the thickness of the Zinc interlayer,the amount of continuously distributed Al₁₂Mg₁₇ decreased and the homogenization degree of their microstructure improved in the transition zone formed in deep melt jiont.When the thickness of Zinc interlayer was 0.1mm,the tensile-shear strength reached 700 N and the fracture occurred at the Mg/Al interface with a mixed fracture morphology.For the metastalbe-welding joints,with the increase of the thickness of the Zinc interlayer,the homogenization degree of their microstructure improved and the thickness of the Al₁₂Mg₁₇ layers decreasing,and the MgZn compounds along the grain boundaries were formed in the fusion area on the Mg side.When the thickness of the Zinc interlayer is 0.15 mm,the tensile-shear strength reached 1274.4N.The fracture occurred near the fusion zone on the Mg side with obvious ductile fracture morphology.Meanwhile,the microhardness on the Mg side indicated a reduced fluctuation.For the joints of heat conduction mode,with the thickness of the Zinc interlayer increasing the amount of Mg-Al IMCs formed in the bottom reduced obviously and the formation of Mg-Zn IMCs hindered the previous continuous distribution of the Mg-Al IMCs layers.When the thickness of the interlayers was 0.1mm,the tensile-shear strength was 626.1N with a mixed fracture.?3?The calculation results of ductile-brittle and the thermodynamic of compounds showed that the Mg/Al direct welding,the weld easily generated brittle phase Al₁₂Mg₁₇ which was stiffness and hardness,large deformation capacity.Adding Zinc interlayer welding,the weld easily generated ductile MgZn2 and MgZn compounds.So,the test results showed that the Mg-Zn compound produced in the weld improved the continuous distribution of Al₁₂Mg₁₇,reduced the degree of embrittlement of the joints,and improved the mechanical properties of the joints.In the direct welding of Mg/Al,the Al₁₂Mg₁₇ and Al₃Mg₂ produced in the weld could be stable,and the thermodynamic stability of MgZn formed by adding Zinc interlayer was better,so the eutectic structure of ?-Mg and MgZn is formed in the weld under this condition.